The present invention relates to processing tomatoes into paste, sauce or related products, in which the processed products have an improved flavour. More in particular, the processed products have increased amounts of fruity flavour compounds.
Processing tomatoes to prepare tomato paste, pasta sauce, etcetera usually involves comminuting tomatoes, heating to inactivate cell-wall degrading enzymes, such as polygalacturonase (PG) and pectin methyl esterase (PME), and heating to remove water (by evaporation) to obtain the desired thickness. The cutting operation and further processing (heating) liberates and induces generation of flavour and aroma compounds. If one plots a graph of the development of flavour intensity over time, (roughly speaking) three peaks can be distinguished, although the bases of the curves overlap with each other.
Early in processing a mixture of predominantly xe2x80x9cgreenxe2x80x9d flavours develops, of which the intensity gradually builds to a peak, whereafter the xe2x80x9cgreenxe2x80x9d flavours gradually disappear, as they are volatile and heating is effected in the processing. Said heating starts the formation of xe2x80x9cburntxe2x80x9d flavour notes, which also builds to a peak in intensity during the processing, albeit usually lower and broader, depending on e.g. processing conditions. In between these two peaks a third peak of xe2x80x9cfruityxe2x80x9d flavours (also sometimes referred to as xe2x80x9ccooked tomatoxe2x80x9d flavours) can be distinguished, although in most processing operations its peak of intensity is much lower than the xe2x80x9cgreenxe2x80x9d and xe2x80x9cburntxe2x80x9d flavours, which are still/already present.
Hence, processing tomatoes on an industrial scale leads to a flavour development over time in which the intensity of the desired xe2x80x9cfruityxe2x80x9d (and/or xe2x80x9ccooked tomatoxe2x80x9d) flavours is usually very much dominated by xe2x80x9cgreenxe2x80x9d and/or xe2x80x9cburntxe2x80x9d notes that are present.
An important xe2x80x9cfruityxe2x80x9d flavour in the above (which is generated in tomatoes) is known to be xcex2-ionone. Similar known in this respect is xcex2-cyclocitral. R. G. Buttery et al report in J. Agric. Food Chem. Vol. 38(1), pp. 336-340 (1990) that xcex2-ionone is present in fresh tomatoes and in tomato paste in concentrations of about 4 and 2 (0-4) ppb, respectively. Similarly, it is reported that xcex2-cyclocitral is present in fresh tomatoes and in tomato paste in concentrations of about 3 and 3 (2-6) ppb, respectively.
U.S. Pat. No. 5,705,372 discloses the preparation of flavour compounds by an enzymic process, in which a source having lipoxygenase and hydroperoxide lyase activity is contacted with unsaturated fatty acids and carotene. The resulting flavour mixture comprises both C6-C10-aldehydes and ionones.
In Sciences Des Aliments, 11, 277-290 (1991) it is disclosed by M Cabibel and J. Nicolas that isolated lipoxygenase from tomato origin can oxidise pigments like xcex2-carotene, when in the presence of linoleate.
It is reported by C. L. Allen and J. W. Gramshaw in xe2x80x9cSpecial Publications of the Royal Society of Chemistryxe2x80x9d Vol. 197, 32-37 (1996) that lipoxygenase isolated from tomato fruit can catalyse the oxidation of linoleic acid in the presence of xcex2-carotene. The major co-oxidation products are reported to be xcex2-ionone, xcex2-cyclocitral, and 5,6-epoxy-xcex2-ionone.
P. Winterhalter (Biotechnology for Improved Foods and Flavours, chapter 28: Carotenoid-Derived Aroma Compounds: Biogenic and Biotechnological Aspects) discloses that lipoxygenase can co-oxidise polyunsaturated compounds and polyene compounds. The polyene compounds can be (derived from) natural sources rich in carotenoids, such as palm oil or plant extracts (e.g. carrots).
U.S. Pat. No. 3,826,851 discloses that the flavor of processed tomato products can be improved by the addition of a mixture composed of cis-3-hexenal, 2-methylhept-2-en-6-one, eugenol, and xcex2-ionone.
It is an object of the present invention to provide a process for preparing a processed tomato product, which tomato product should have an enhanced xe2x80x9cfruityxe2x80x9d flavour (flavour is to be understood herein to include aroma next to taste), when compared to conventional processing. Said process should preferably involve minimal changes in conventional tomato processing to provide a processed tomato product (e.g. paste, pasta, passata, salsa, sauce, dices, pulp etcetera). Any changes in processing involving the addition of specific components should preferably be such that the added components are food grade and/or are of tomato-origin. It is a further object of the present invention to provide a processed tomato product having an enhanced xe2x80x9cfruityxe2x80x9d flavour.
It has been found that the above objectives can be achieved by a process for preparing a tomato product, the process comprising at least the steps of:
comminuting tomatoes,
adding a source providing solubilised or soluble carotenoids
adding a source providing poly-unsaturated fatty acids, incubating the above mixture for at least 10 minutes.
In this process, the tomatoes before being incubated should preferably treated such that not all endogenous enzymes are being inactivated.
Alternatively, such a product may be obtained by a process for preparing a tomato product, the process comprising at least the steps of:
comminuting tomatoes,
solubilising carotenoids present in said tomatoes,
adding a source providing poly-unsaturated fatty acids,
adding an enzyme preparation having lipoxygenase (EC 1.13.11.12) activity, incubating the above mixture for at least 10 minutes.
It was found that the above processes, which rely on the same principle, provide a processed tomato product having a concentration of xcex2-ionone of at least 10 ppb (parts-per-billion).
Likewise, to further improve the fruity flavour of the processed tomato product, it is preferred to provide a processed tomato product having a concentration of xcex2-cyclocitral of at least 10 ppb (parts-per-billion). The above can be achieved by the same processes as disclosed above.
The term xe2x80x9cprocessedxe2x80x9d is herein to be understood as to refer to any product obtained by comminuting fresh tomatoes, but preferably not (sun-)dried tomatoes.
In the above, it is in particular preferred if the processed tomato product is a tomato pasta, tomato passata, tomato salsa, tomato ketchup, pulped tomato, diced tomato, tomato juice, tomato soup, etcetera.
In the processes as disclosed above, polyunsaturated fatty acids (PUFA""s) may be added as such or in the form of triglycerides of PUFA""s. Considering the latter case, most PUFA-triglyceride sources such as olive oil contain a considerable amount of free fatty acids, among which are free PUFA""s. When adding triglycerides, it is also possible to liberate the PUFA""s therefrom, provided that in the latter case an enzyme having lipolytic activity is present or is added.
In the first process as described above, one source providing both carotenoids and poly-unsaturated fatty acids may be used to provide both components partly or fully. An example of such a source is vegetable oil rich in carotenoids, such as olive or or palm oil.
Although two processes are set out above, the essence of the invention can be seen in the following process:
comminuting tomatoes,
adding a source providing poly-unsaturated fatty acids,
ensuring solubilised or soluble carotenoids are present
ensuring an enzyme having lipoxygenase (EC 1.13.11.12) activity is present
incubating the above mixture for at least 10 minutes. Some of the compounds (e.g. the enzyme or carotenoids) can be present by nature in tomatoes, and is it a mere xe2x80x9cmaking them availablexe2x80x9d (carotenoids) or activation (enzyme).
To further improve the fruity flavour of the processed tomato product, it is preferred to provide a processed tomato product having a concentration of xcex2-ionone of at least 30 ppb (parts-per-billion). More preferably the concentration of xcex2-ionone is at least 100 ppb.
Depending upon the source and intended product, it may be preferred to have processed tomato products which are both high in xcex2-ionone and xcex2-cyclocitral, in concentrations as above. Preferred concentrations for xcex2-cyclocitral are at least 20 ppb, preferably at least 100 ppb.
Although no real upper limits for the presence of the fruity components as xcex2-ionone and xcex2-cyclocitral exist, this will usually be less than 1000 ppm for each of these components, but usually less, although this depends on the product concenrned (e.g. concentrated tomato paste vs tomato juice).
Although the processes as set out above may provide other valuable (carotenoid derived) fruity flavours in addition to xcex2-ionone and xcex2-cyclocitral, these two components (and in particular xcex2-ionone) are chosen as yardstick and are very characteristic of fruity and/or cooked flavours.
For example, under similar conditions linear terpenoids can be co-oxidised by lipoxygenase in the presence of PUFA""s to form other compounds contributing to the overall fruity flavour, e.g. geranyl acetone.
Although two alternative processes are set out above, the 10 present invention also covers combinations of the two processes, provided that:
an enzyme having lipoxygenase activity is present
xcex2-carotene is present in a soluble/solubilised form
a polyunsaturated fatty acid is present or can be generated in-situ (e.g. from triglycerides and a lipolytic enzyme). Intermediate forms of both processes (e.g. both adding an enzyme as well as activating the lipoxygenase already present) are also covered by the present invention.
The carotenoids play an important role in the co-oxidation process as presently claimed. Although most tomato varieties contain carotenoids in a sufficient amount, most of it is believed to be located in the form of crystalline regions in chromoplasts, which is a form unsuitable to play a role in the co-oxidation. Hence, in order to provide sufficient available carotenoids it is necessary that carotenoids already present are solubilised, are added in already soluble or solubilised form, or both. Solubilisation (e.g. in a hydrophobic phase) can be achieved by techniques known in the art involving a surfactant or emulsifier, where appropriate.
In the process for obtaining the above products, it is preferred that the incubation is carried out at a pH of between 3 and 7. More preferably the incubation is carried out at a pH of between 4 and 6.8. Most preferred is to effect the incubation at a pH the comminuted tomato already has (e.g. 4-5 or 4-4.5). This avoids the use of acidifiers or alkali.
In view of the optimum of the enzyme having lipoxygenase activity, it is preferred that the incubation is carried out at a temperature of 10-90xc2x0 C., preferably 50-80xc2x0 C. conveniently, such temperatures are quite similar to the temperatures applied in normal processing (cold break).
Best results (in terms of desired flavour formation) can be achieved if lipoxygenase is allowed to perform, whilst hydroperoxide lyase activity (of which some is usually present in tomatoes) is kept low, preferably as low as possible. As hydroperoxide lysase is inactivated at a much lower temperature than lipoxygenase (difference about 25-30xc2x0 C.), hydroperoxide lyse can be inactivated by heating (e.g. to 50xc2x0 C. for 15 minutes). By doing so, the amount of C6-C10 aldehydes formed is minimal, and it is these compounds which can dominate the fruity flavour with their xe2x80x9cgreenxe2x80x9d character.
In actual processing tomatoes the processes as set out above can be carried out at various stages of processing, e.g:
after comminuting but before the actual hot- or cold-break process (and by ensuring the substrate and co-substrate are present)
in the processed tomato product, by adding an enzyme having lipoxygenase activity (and by ensuring the substrate and co-substrate are present).
Also, it is possible to have the processing carried out split stream. One stream in which fruity flavours such as xcex2-ionone and xcex2-cyclocitral are generated according to the present invention, and one stream of tomatoes which is subjected to normal tomato processing, such as the conventional hot- or cold-break process. The two streams may then later be mixed, the first to provide the fruity flavour, the second providing the bulk and/or body of the processed tomato product.